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Let \(r\) be the positive real solution to \(x^3 + \frac{2}{5} x - 1 = 0.\) Find the exact numerical value of \(r^2 + 2r^5 + 3r^8 + 4r^{11} + \dotsb.\)
 

 

Thank You!

 Jan 5, 2020
edited by NewMember  Jan 5, 2020
 #1
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From the formula for a geometric series, the sum is 19/3.

 Jan 5, 2020
 #2
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Let \(r\) be the positive real solution to \(x^3 + \dfrac{2}{5} x - 1 = 0\).
Find the exact numerical value of \(r^2 + 2r^5 + 3r^8 + 4r^{11} + \dotsb\) .

 

answer see: https://web2.0calc.com/questions/math-question_148#r2

 

laugh

 Jan 6, 2020

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